1. Technical Field of the Invention
This invention relates to the manufacture of enamines from conjugated dienes. More particularly, this invention relates to a method wherein a conjugated diene, such as 1,3-butadiene is reacted with a secondary amine and also with carbon monoxide and hydrogen (synthesis gas) at an elevated temperature and under appropriate pressure in the presence of a rhodium-containing catalyst to substantially selectively convert the conjugated diene to an enamine.
2. Prior Art
It is known that organic amines can be prepared from enamines by Diels-Alder reactions, Michael-type reactions, reduction reactions, etc. There is a need, therefore, for improved methods for the preparation of enamines.
The enamines are versatile intermediates in organic synthesis, for example, a general method for preparing enamines from a carbonyl compound, an aldehyde or ketone, with a secondary amine and the synthetic applications of enamines such as alkylation or acylation have been reported by G. Stork et al., JACS, 85, 207 (1963). Review articles, Tetrahedron, 33, 609 (1977) and Tetrahedron, 38, 3363 (1982), cover developments in the methods of preparation of enamines and the reaction of enamines with electrophiles.
Nomura et al. (Bull. Chem. Soc. Jpn. 55, 3343-3344, 1982) disclose the reaction between enamines and Schiff Bases by a cyclo addition reaction such as the reaction between N-benzylideneanilines and 4-(1-phenyl-1-propenyl)morpholine to provide N-(3-aryl-2-methyl-1-phenylallylidene)anilines.
Ishihara et al. (Bull. Chem. Soc. Jpn 55, 3345-3346, 1982) disclose the preparation of enamines from ketones and aldehydes to provide morpholine enamines which are then reacted with hexafluoropropene oxide to provide pentafluorinated 1,3-diketones.
The preparation and reaction of enamines is discussed in Chapter 3 of Volumne 20 of Organic Reactions in an article by George R. Allen, Jr. entitled "The Synthesis of 5-Hydroxyindoles by the Nenitzescu Reaction".
The related synthesis gas reactions of olefins, amines and CO/H.sub.2 in the presence of various catalysts, such as rutheninum, cobalt, iron and rhodium, generally produced amines as the products (namely, aminomethylation). Some examples are discussed as follows. In U.S. Pat. No. 4,292,242 and J. Org. Chem., 1980, 45, 3370-3372, R. M. Laine disclosed the synthesis of tertiary amines from olefins, carbon monoxide, water and amines by using mixed metal hydroformylation catalysts. U.S. Pat. Nos. 4,250,115; 4,356,334 and 4,096,150 and J. Org. Chem., 1982, 47, 445-447, describe the synthesis of tertiary and secondary amines from olefins, carbon monoxide, hydrogen or water and a nitrogen source in the presence of transition-metal compounds as catalysts, including rhodium.
The synthesis of dienamines intermediately from the reaction of butadiene, an amine, and CO/H.sub.2 using a rhodium catalyst under mild pressure and temperature has not been disclosed.